In video projectors, the image generation is based on targeted switching on and off of individual pixels of a light beam with the aid of an imaging optical system (“imager”), e.g. on the basis of a DLP (“Digital Light Processing”), LCD (“Liquid Crystal Display”) or LCoS (“Liquid Crystal on Silicon”) technology. In order to represent a specific color, light from a light source with broadband emission (e.g. a discharge lamp) is decomposed into its primary colors (e.g. by means of a rotating color wheel with corresponding color filters), which are then alternated sequentially in the necessary power proportions usually using a single imager (in the case of DLP technology, for example, as so-called single-chip DLP technology). This also applies, in particular, to the representation of “white”. Assuming that three primary colors (e.g. red, green and blue) are alternated with the temporal proportion of in each case a respectively defined temporal proportion of in each case one third, for example, correspondingly each of the three sequentially active primary color channels is also utilized only during this time proportion. This results in the disadvantage that the luminous flux utilized amounts to only a portion, for example one third of the luminous flux that is technically maximally available (in which case all three primary color channels would be utilized to the extent of 100%).
In order partly to resolve this disadvantage, the color wheel can also contain a transmitted-light segment having a high transmission which is not wavelength-dependent (“white segment”). The size of the white segment is fixedly predefined by the technical implementation and then can no longer be changed during the operation of the video projector. Owing to this restriction, it is necessary to optimize the color wheel once by means of the segment division for a specific type of application of the projector (e.g. for a data projection with high areal proportion of white or a projection of image material with a high color saturation).
A dynamic adaptation of the power with regard to the individual color proportions in the sequential mixed light can be effected by the so-called Unishape method from Osram, in which the power consumption of a mercury vapor lamp and thus the luminance in the arc of the mercury vapor lamp is varied very rapidly in a manner synchronized with color segments of a color wheel, that is to say that the lamp is operated briefly with lower or higher power. In this regard, lighting properties such as color proportions, brightness, etc. can be adapted. In single-chip DLP projectors, a color temperature and a color saturation can thus be significantly increased by this method. However, the length of the color segments cannot be varied in this case.
Furthermore, video projectors are known which use semiconductor light sources and phosphor conversion in order to generate a sequential succession of the primary colors.